1. Field of the Disclosure
The invention generally relates to scratch-resistant coatings, to substrates having scratch-resistant coatings, and to methods for producing such coatings. More particularly the invention relates to scratch-resistant coatings and coated substrates having a hard material layer based on aluminum nitride, and to the manufacturing thereof, in particular by sputtering.
2. Description of Related Art
Various coatings for increasing scratch resistance are known from prior art. For example, patent application DE 10 2011 081 234 A1 describes a hard material coating on glass ceramic substrates, which has two different material phases. However, a disadvantage thereof is that the coefficient of thermal expansion of the coating and of the substrate must not differ by more than 20%. Moreover, since glass ceramics have a very low coefficient of thermal expansion, this considerably limits the number of suitable coatings. For example, the coefficient of thermal expansion of hard material layers based on nitrides or oxides, such as aluminum nitride or boron nitride is too high, so that these materials cannot be used for coating glass ceramic substrates.
A coating for enhancing scratch resistance should not only have a high hardness. Rather, other decisive factors for the quality of a scratch-resistant coating or of a substrate coated therewith include elasticity (modulus of elasticity), surface roughness, layer tensions due to different coefficients of thermal expansion of the substrate and the coating, and surface properties of the substrate.
Moreover it is desirable that in addition to high scratch resistance surfaces coated accordingly such as glass or glass ceramic surfaces exhibit high resistance to wearing and polishing stress which occurs during manufacturing and also during subsequent use.